1. Field of the Invention
The present invention relates generally to an optical storage system and, in particular, to a read channel apparatus for an optical storage system.
2. Description of the Related Art
In recent years, the development of new optical recording media and data compression techniques has made it possible to achieve enormous data storage capacity using optical storage systems. Optical storage systems are used to store audio information, such as in Compact Disk (CD) players, as well as visual and computer information, such as in CD-ROM and the more recent Digital Video Disk (DVD) players. The information is typically recorded as a binary sequence by writing a series of “pits” on the optical medium which represent binary “1” and “0” bits. When reading this recorded data, a pick-up head (transducer), positioned in close proximity to the rotating disk, detects the alternations on the medium and generates an analog read signal. The analog read signal is then detected and decoded by read channel circuitry to reproduce the recorded data.
To improve performance of the read channel in an optical storage system, the sampled amplitude techniques are applied. Sampled amplitude read channels commonly employ an analog-to-digital converter (ADC) and a digital read channel processor to reproduce data recorded on the optical storage systems. However, in high-speed optical storage systems, the baud rate (channel bit rate) is very high such that sampling frequency of ADC and clock of digital processor also need comparable high clock rate sources. This is not desirable since operating the channel at higher frequencies increases its complexity and cost. There is, therefore, a need for a sampled amplitude read channel for use in storage systems that can operate at high data rates and densities without increasing the cost and complexity of the read channel ICs. To this end, U.S. Pat. No. 5,802,118 (Bliss et al.) discloses a sub-sampled discrete time read channel for magnetic disk storage systems. According to this patent, the read channel sub-samples an analog signal at a rate less than or equal to 9/10 the baud rate. K. C. Huang, the inventor of present invention, discloses a sub-sampled method for read channel of an optical storage system in Taiwan patent application No. 089,110,848, filed in June 2000. The prior art sub-samples an analog signal at a rate slightly above ½ the baud rate. The sub-sampled values are down-sampled by a timing recovery interpolator to generate sample values synchronized to one-half the baud rate. The synchronous sample values are then equalized by a 2T-spaced equalizer and interpolated by a factor-two upsampler. Although it significantly reduces the sampling frequency, the latency time introduced by the upsampler causes significant degradation in the performance of the high-speed optical storage systems.
For the reasons mentioned above, a novel read channel apparatus and method is provided to reproduce data recorded on the optical storage systems, unencumbered by the limitations associated with the prior art.